At present, cumene output in the world reaches nearly ten million tons, and more than 90% of the cumene are used to produce phenol and acetone. In this process, α-methyl styrene (AMS), a byproduct, is generated generally, and it is difficult to separate and remove AMS in subsequent refining procedures. However, AMS can be converted into raw material cumene by hydrogenation, and the raw material cumene can be used again in an oxidation procedure. By doing this, unit consumption of cumene can be reduced; a yield coefficient of phenol can be improved; and cost of raw materials can be saved. In this way, not only consumption of propylene and benzene raw materials can be reduced, but also technical and economic indexes of a device can be improved.
500 tons of AMS may be generated as a byproduct by a device for producing phenol/acetone with an annual output of 10000 tons, and devices for producing phenol/acetone used abroad all comprise an AMS hydrogenation unit. A traditional method of producing cumene by AMS hydrogenation is a slurry process, in which a Reney nickel catalyst is used, but the slurry process has defects such as complicated procedures, low selectivity of catalysts and a short usage cycle. The slurry process is gradually replaced by a fixed bed process. Performance of hydrogenation catalysts are very critical for the fixed bed process. There are many reports on catalysts for producing cumene by AMS hydrogenation. Saito studied experiments of catalytic hydrogenation to AMS using platinum as a catalyst. Phenolchemie Co. used Cu2Cr2Ni to perform AMS hydrogenation. Chongheng He studied high-temperature thermal sintering of a palladium/alumina catalyst. Franco C et al. used a Pd/C catalyst in α-Methyl styrene hydrogenation. Little et al. respectively studied AMS selective hydrogenation properties of Ni, Pt, Pd, Co, Cr2O3 and several metal alloy catalysts. Activity and selectivity of non-palladium catalysts are not high, and catalysts which comprise palladium as a main or unique ingredient receive great attention in recent years. AMS is chemically active and has poor stability. Therefore, it is hoped that a hydrogenation catalyst has higher low-temperature activity and selectivity, as well as proper impurity-resistance property so as to increase a regeneration cycle of the catalyst, thereby prolonging the service life of the catalyst.
U.S. Pat. No. 3,646,235 discloses a use of nickel, platinum, palladium, cobalt, chromium oxides and mixed metal catalysts in AMS hydrogenation. Under conditions of a temperature of 24-50° C. and a pressure of 0.17-0.45 MPa, a Pd catalyst with metal content of 1-5% (by weight) is better.
Chinese patent CN1793089A discloses a method for selective hydrogenation of AMS to cumene by using a combined catalyst system having a nickel catalyst and a noble-metal catalyst. In the method, a combination of commercially available catalysts is packed, 70-95% of AMS conversion in a first reaction zone was achieved and at least 95% of AMS conversion in a second reaction zone was achieved.
There is a need for a novel catalyst used for production of cumene which has an improved AMS conversion rate and cumene selectivity.